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Learn about constellations, navigation using stars, the importance of the North Star Polaris, and why stars appear to move. Discover how Earth's rotation and revolution affect the night sky and the changing shapes of constellations.
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What is a constellation? • A group of stars forming a recognizable pattern that is traditionally named after its apparent form or identified with a mythological figure. • 88 constellations
History in Constellations • https://www.youtube.com/watch?v=QXeEAQtC75g
Stars were used for Navigation • ancient sailors watched constellations to mark their position.
Importance of the North Star • Polaris, or the North Star, sits almost directly above the North Pole; therefore, it is a reliable gauge of North if you find yourself lost on a clear night without a compass.
Why do stars appear to revolve around polaris? • As the Earth spins on its axis, it also “spins around” the north celestial pole. • Earth's axis points almost directly to Polaris, so this star is observed to show the least movement. • The other stars appear to trace arcs of movement because of Earth's spin on its axis • When looking north, objects in the sky move counter-clockwise.
Will Polaris always be our North Star? • Even though Polaris is the North Star today, this has not always been the case. • The place in the sky that the Earth’s north pole points at changes slowly over time (stellar precession). • In 3000 BC, a faint star called Thuban in the constellation of Draco was the North Star. • The Earth’s axis slowly rotates in a circle every 26000 years .
Polaris, the North Star, lies at the end of the handle of the Little Dipper.
Star Chart • A star chart or star map, is a map of the night sky.
Practice: Make your own Star Map • http://www.cupcakesandthecosmos.com/2016/11/how-to-use-a-star-chart/
https://www.artofmanliness.com/articles/15-constellations-every-man-should-know/https://www.artofmanliness.com/articles/15-constellations-every-man-should-know/
Stars move through space • In addition to their apparent motion, stars are moving through space. • Because the stars are so far away, it is difficult for us to see their motions. • Over thousands of years, however, the movements of the stars can cause the shapes of constellations to change.
Do Stars Move? • Stars move, but because they are so far away and move so slowly, we cannot see their movement easily. • Every night stars seem to rise and set, but it is not the stars that are moving. It is the Earth. • The rotation of Earth causes daytime and nighttime. • Because of Earth’s rotation, the sun moves across the sky during the daytime. For this same reason, the stars seem to move across the sky at night. • All of the stars that you see appear to rotate around Polaris, the North Star. The stars seem to make a full circle around Polaris every 24 hours. • Earth’s tilt and revolution cause the seasons. • During each season, any point on Earth faces a different part of the sky at night. That means that different stars appear in the night sky at different times of the year.
